The present invention generally relates to environmental control in semiconductor manufacturing operations, including management of airflow in controlled environments and containment and capture of hazardous fume species. More particularly, the present invention relates to improved chemical containment and contamination reduction apparatuses, systems, and processes in semiconductor manufacturing facilities. In a specific aspect, the invention relates to a chemical containment apparatus for capturing and reducing hazardous chemical fumes released by chemical tanks used in a semiconductor wet processing system.
Semiconductor manufacturing must be performed in a particle-free environment, due to the fact that submicron size dimensions characterize the structural elements of the electronic circuitry, and that such circuitry can be rendered inoperative by the presence of even a single particle of dust. Semiconductor manufacturing process steps are therefore carried out within the confines of a clean room, which is a controlled environment through which an exhaust system continuously flows large amount of filtered air to remove dust, lint, and other particulate matter.
On the other hand, many semiconductor manufacturing process steps involve the use of chemicals that are toxic or otherwise hazardous to humans, which also necessitates use of localized exhaust equipment to contain, remove, or otherwise abate fumes from such chemicals.
Typically, efficiency of an exhaust system (i.e., the exhaust energy necessary to remove hazardous chemical fumes in a particular environment) is a function of two independent factors: the station exhaust (xe2x80x9cpullxe2x80x9d force) and the laminar airflow from the clean room ceiling (xe2x80x9cpushxe2x80x9d force). These two motive forces of airflow form a push-pull system, which is the basis for system exhaust operation.
Exhaust efficiency can in one aspect be characterized by Ce (Coefficient of Entry), which is defined by the American Conference of Governmental Industrial Hygienists as:
xe2x80x9cThe actual rate of flow caused by a given hood static pressure compared to the theoretical flow which would result if the static pressure could be converted to velocity pressure with 100% efficiency. The ratio of actual to theoretical flow.xe2x80x9d
Maximum possible exhaust efficiency is achieved when Ce=1.0. Typical Ce values range from 0.2 to 0.7 (for highly efficient exhaust systems). In general, the greater the distance between the air inlet and exhaust outlet, the smaller is the value for Ce.
If unobstructed, ceiling-to-floor laminar airflow in a clean room loses relatively little volumetric flow velocity and therefore has relatively higher Ce value. Typically, an 80 feet per minute (fpm) laminar air stream as measured at the ceiling is slightly attenuated to approximately 71 fpm at the deck level, away from semiconductor processing equipment and systems below the deck. When such air stream is pulled further down to beneath the deck level, semiconductor processing equipment, most notably chemical tanks, obstruct flow path for such air stream and induce air turbulence in their vicinity. The air stream is bent or separated by the obstructing objects, and volumetric flow velocity of such air stream is reduced to a level that is too low to fully contain and remove chemical fumes.
Because of these factors, conventional exhaust systems exhibit marginal fume capture capability, and many fail to consistently control contamination and hazardous fumes under the deck, resulting in occasional fumes spills into the process and operator environment.
Critical Capture Velocity (CCV) is generally used in characterizing minimum fume capture capacity required for an exhaust system in a clean room environment. CCV is defined as the minimum airflow velocity measured over a process tank at which fumes will be controlled below the station deck. A properly balanced system can achieve this velocity (empirically determined to be at values of 70 fpm or greater) with a combination of exhaust flow rate, laminar airflow, and minimal deck opening size, if enough exhaust capacity is available.
As wafer sizes used in the semiconductor industry grow to 300 mm or more and require larger deck openings, however, CCV becomes more difficult to achieve, and facility exhaust capacity is stretched beyond its limits. Conventional push-pull systems will not be able to produce enough combined force to achieve capture of hazardous fumes in large size wafer facilities now under design and construction.
Additionally, the exhaust systems in many 200-millimeter (mm)-facilities in current use are unable to achieve CCV because of a disparity in the exhaust capacity, deck opening sizes, and laminar push. Consequently, fume spill incidents occur in many wafer fabs, resulting in yield loss, excessive rework, process disruption, environmental and regulatory noncompliance, injury, and litigation. Additionally, the economics of the semiconductor market demand a reduction in overall production costs as semiconductor fabs move to larger wafer sizes. The international semiconductor industry association SEMATECH has determined a need to reduce exhaust energy consumption by a magnitude of 35 to 40% from current average levels, even as progressively increasing wafer sizes necessitate larger, higher capacity, higher energy consumption exhaust systems.
It would therefore be a significant advance in the art: (i) to provide an improved air management system, with increased efficiency for containing hazardous chemical fumes and reducing fume spill, while consuming less energy; (ii) to provide an air management system for chemical containment and contamination reduction, which assures maintenance of CCV at values of 70 fpm or greater; and (iii) to increase the Ce of exhaust equipment toward a value of unity.
In the fabrication of semiconductor wafers, a multitude of cleaning steps is required to remove impurities from the surface of the wafer prior to subsequent processing. Generally, a batch of wafers is dipped into one or more chemical tanks that contain chemicals that are needed for clean or etch functions.
A serious problem associated with such immersion wet cleaning process is that the liquid chemicals contained by the chemical tanks release hazardous fumes at their surfaces. Such fumes tend to migrate to the environment surrounding the tanks and pose environmental hazards or cause worker injuries.
Containment of hazardous chemicals in semiconductor wet processing systems is done today using below-deck exhaust systems, which function to capture chemical fumes or keep them at or below the deck.
In order to effectively keep hazardous chemicals under control and out of the workspace above the deck, the below-deck exhaust systems have to effectuate flow of large volumes of filtered air through the wet cleaning tools at very high rates, e.g., on the order of 150 cubic feet per minute (cfm). High capacity exhaust systems are expensive, energy-consuming, and difficult to install and maintain.
Moreover, pressure fluctuations in the exhaust air stream or in the semiconductor processing system overall still cause deleterious turbulence and loss of fume control at certain localities in the system, resulting in formation of xe2x80x9cplumesxe2x80x9d of hazardous vapors.
Some wet processing systems employ safety lids as supplemental means for fume control. The safety lids isolate each chemical tank from the environment to reduce migration of hazardous chemicals into workplaces. They also function to reduce dissipation of useful chemicals due to migration of fumes.
Commonly used safety lids include clamshell type and drawbridge type lids. Such lids significantly reduce the flexibility of wet processing systems as well as the wafer throughput. The opening and closing of such lids still results in local turbulence. Accordingly, such lids cannot completely eliminate escape of chemical fumes from the chemical tank. Moreover, currently available safety lids are mechanically complex, expensive, and difficult to maintain. Further, hazardous chemical vapors tend to condense on the bottoms of the safety lids, which may result in more severe worker injuries or potential environmental problems.
It therefore would be a significant advance in the art to provide a chemical containment apparatus that is economic, easy to install and maintain, energy saving, and more effective in fume control than the conventionally available alternatives. Moreover, it would be advantageous to have a chemical containment apparatus that presents minimal limitation on the flexibility of the wet processing systems, and that does not cause condensation of chemical vapors in its vicinity.
The present invention relates to environmental control systems useful in semiconductor manufacturing operations.
The present invention in one aspect provides active filtered airflow xe2x80x9cpushxe2x80x9d elements, located proximate to a fume-releasing liquid chemical tank, and in such a position as to direct filtered airflow across the surface of such tank, thereby capturing hazardous fumes rising therefrom. Directed airflow may be filtered to an efficiency of 99.9999%.
The present invention in one specific apparatus aspect relates to an air manager, positionable in relation to a chemical tank containing chemical emitting fumes, for entraining fumes and preventing their escape, such air manager comprising:
an airflow source constructed and arranged to generate an air stream; and
an airflow exhaust comprising an exhaust inlet for receiving the air stream;
wherein the airflow source and the airflow exhaust are positioned in relation to one another so that the air stream generated by the airflow source passes across an upper surface of the chemical tank, whereby fumes produced at the surface of the chemical tank are captured by and entrained in the air stream, and transported to the airflow exhaust.
In a semiconductor manufacturing facility in which the chemical tank is below a deck, the air stream flowed across the open chemical tank is maintained below the deck as well.
The air manager may be embodied in a structural assembly comprising a plate member having air source and air exhaust members mounted thereon, whereby the air manager may be employed as a retrofit apparatus for existing semiconductor manufacturing facilities, e.g., in an open architecture wet bench facility.
In a specific aspect, the air manager of such type, installed in an open architecture wet bench facility and with the air source member incorporating or arranged for connection to a high purity air supply, may be employed to provide a level of cleanliness approaching that routinely achieved by far more expensive mini-environment wet bench facilities.
In yet another aspect, a wet bench facility including an open topped chemical tank is shrouded by air manager units of the type described hereinabove, to provide a xe2x80x9cvirtual wallxe2x80x9d containment of the fumes from the tank, wherein each virtual wall includes an air source and an air exhaust, arranged to produce a generally flat airstream bordering a perimeter area of the chemical tank or the wet bench itself.
Another aspect of the invention relates to a scroll lid assembly for preventing chemical fumes from escaping from a semiconductor wet processing system, including:
a thin film member including at least one solid portion and at least one cut-out portion;
a first scroll member positioned at a first side of the thin film member for rotatorily moving the thin film member;
a motive driver operatively connected to the first scroll member for rotating the first scroll member; and
optionally, a second scroll member positioned at a second side of the film member for rotatorily receiving the thin film, in synchrony with rotatory movement of the first scroll member.
Such scroll lid assembly is useful as a chemical containment apparatus in various areas of semiconductor manufacturing processes that use hazardous liquid chemicals.
In one aspect of the present invention, such scroll lid assembly is incorporated in a chemical tank assembly of a semiconductor wet processing system, which includes:
a chemical tank arranged to contain a liquid chemical producing deleterious chemical fumes at its upper surface; and
at least one scroll lid assembly as described hereinabove, positioned above the chemical tank, for reducing escape of chemical fumes from said chemical tank into a surrounding environment.
Such chemical tank assembly may also incorporate an air manager as described hereinabove to prevent deleterious condensation of chemical fumes underneath the thin film member of the scroll lid assembly, wherein the air manager may be placed between the scroll lid assembly and the chemical tank below it.
A further aspect of the present invention relates to a wet station assembly of a semiconductor manufacturing facility. The wet station assembly includes a liquid chemical tank, a deck positioned above the tank and having an opening over the tank for ingress and egress of semiconductor manufacturing workpieces, a laminar downflow air source, a below-deck exhaust, and a below-deck airflow source positioned in relation to the below-deck exhaust to flow an air stream over a surface of liquid in the liquid chemical tank at a sufficient rate and in a sufficient volumetric flow to achieve Critical Capture Velocity (CCV) of vapor released from the liquid during operation of the wet station assembly. The below-deck airflow source of such wet station assembly may comprise an air plenum member including a purification medium and a motive air driver for effecting flow of air from the plenum member across the liquid surface of the liquid chemical tank. The wet station assembly can further comprise a scroll lid assembly as described hereinabove, which is positioned below the deck, and above the liquid chemical tank and the below-deck airflow source.
Yet another aspect of the present invention relates to an open architecture wet processing station of a semiconductor manufacturing facility, comprising:
a wet bench including one or more chemical tanks containing liquid chemicals that produce deleterious chemical fumes at their surfaces;
an exhaust situated in relation to the chemical tank for capturing at least a portion of the deleterious chemical fumes by suction; and and
at least one environmental management system, selected from the group consisting of air managers and scroll lid assemblies, positioned to substantially prevent escape of the chemical fumes from the vicinity of the wet bench.
Preferably such open architecture wet processing station comprises at least one scroll lid assembly as described hereinabove. One or more air managers may be employed in such open architecture wet processing station, for further capture of chemical fumes that escape beyond the scroll lid assembly. The filtered airflow source and the airflow exhaust of each air manager are positioned in relation to one another so that the air stream generated by the filtered airflow source functions as an air wall outside and adjacent to at least one chemical containment apparatus to capture chemical fumes escaping barriers formed by the chemical containment apparatus.
In one specific embodiment of the present invention, the open architecture wet processing station comprises air manager units, one of which is positioned in an open front portion of the wet bench, one of which is positioned at a first side of the wet bench and a second one of which is positioned at a second side of the wet bench, so that air streams generated by these air, managers form an xe2x80x9cair wallxe2x80x9d enclosure for capturing chemical fumes, in operation of the wet bench.
A still further aspect of the present invention relates to an open architecture wet processing station comprising one or more air managers, wherein each air manager comprises:
an airflow source constructed and arranged to generate an air strewn; and
an airflow exhaust comprising an exhaust inlet for receiving said air stream;
wherein the airflow source and the airflow exhaust are positioned in relation to one another so that the air stream generated by the airflow source functions as an air wall outside and adjacent to a source of chemical fumes in said station.
The present invention also relates to a method of containing hazardous fumes emanating from the surface of a liquid chemical in a liquid chemical tank, comprising the steps of. (1) providing an airflow source for generating an airflow and an airflow exhaust having an inlet constructed and arranged to receive the airflow; (2) positioning the airflow source and the airflow exhaust inlet in relation to one another and to the liquid chemical tank, so that airflow from the air flow source flows over the surface of liquid chemical in the liquid chemical tank; (3) flowing an air flow from the airflow source in a generally horizontal stream over the surface of the liquid chemical to the airflow exhaust inlet, whereby substantially all deleterious fumes emanating from the surface of the chemical are captured by and entrained in the airflow, and flow into the airflow exhaust. The airflow can be confined to a region above the surface of the liquid by guide structures at sides of the liquid chemical tank; alternatively, a scroll lid assembly positioned above the liquid chemical tank can confine it.
Another aspect of the invention relates to a semiconductor fabrication facility clean room including a ceiling-to-floor laminar airflow system, an exhaust system, a liquid chemical tank for containing a liquid chemical composition producing fumes from a liquid surface thereof, and an air manager assembly including an airflow source and an airflow exhaust inlet arranged in facing relationship to one another at opposing sides of the liquid chemical tank above the liquid surface, with the airflow source and airflow exhaust inlet being constructed and arranged to maintain airflow across the surface of the liquid chemical from the airflow source to the airflow exhaust inlet at an airflow velocity above the Critical Capture Velocity of chemical liquid fumes from the liquid chemical in the liquid chemical tank.
A still further aspect of the invention relates to a method of operating a semiconductor fabrication facility clean room including a ceiling-to-floor laminar airflow system, an exhaust system and a liquid chemical tank for containing a liquid chemical composition producing fumes from a liquid surface thereof, such method comprising providing a filtered airflow source and airflow exhaust inlet at opposite sides of the liquid chemical tank above the liquid surface, and directing airflow across the liquid chemical surface from the filtered airflow source to the airflow exhaust inlet at an airflow velocity above the Critical Capture Velocity of chemical liquid fumes from the liquid chemical in the liquid chemical tank.
Various other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and claims.